1. Field of the Invention
The present invention relates to an illumination means for a microwave oven cooking cavity and more specifically to an illumination means mounted within the cooking cavity.
2. Description of the Prior Art
Microwave ovens designed for home and commercial use in heating food items require a carefully designed and constructed cabinet structure enclosing the cooking cavity in order to ensure uniform heating throughout the cavity and to avoid leakage of microwave radiation. Since the operator of such an oven must have easy access to the interior of the cavity, a door is generally provided on the front side of the cavity. Further, it is desirable to permit the user to view the interior of the cooking cavity with the door closed, and thus the doors are provided with a transparent, yet shielded area which permits viewing through the door while preventing microwave leakage. Also, a lamp is used to provide illumination within the cavity.
In previous microwave cavity constructions, the lamp is generally mounted on the exterior of the cavity and the light is permitted to enter the cavity through a "window" comprising a plurality of small perforations in the cavity wall. The main reason for mounting the light bulb on the exterior of the cooking cavity is that microwave energy destroys the filaments in a light bulb very quickly and an unprotected bulb would be useless in that it would immediately burn out each time the oven was used. Further, the wiring connecting the bulb with a power source would act as an antenna to radiate microwave energy out of the cooking cavity.
When the light bulb is placed on the exterior of the cooking cavity, not all of the light from the bulb is directed into the cavity, since only the portion of light radiating toward the openings in the cavity wall can enter the cavity. Thus, the wattage of the bulb must be selected which would be sufficient to illuminate the entire cavity to a predetermined level. Such a wattage is necessarily greater than if the bulb were able to be placed within the cavity.
To access an exteriorly mounted bulb for changing, it is generally necessary to remove at least a portion of the outer cover of the oven enclosure. The portion which must be removed is either an outer wrapper or a portion of the back panel. In either case, such a procedure generally requires movement of the microwave oven and perhaps surrounding items.
Often microwave ovens are built into adjoining cabinetry in a kitchen and, when the light bulb is accessible only from the side or rear of the oven, it is necessary to completely remove the oven from the cabinetry in order to change the bulb. Clearly this is a time consuming and difficult operation since microwave ovens are bulky and fairly heavy, sometimes making the changing of a light bulb a project requiring two people.
When the light bulb is placed on the exterior of the cooking cavity, it may not be in the flow path of air which is circulated through the oven. This could lead to a higher than desirable operating temperature for the bulb with a resulting shortened life for the bulb. In such case, the extra effort required for changing the bulb occurs that much more often. This situation is compounded due to the fact that the wattage of the bulb, and thus the heat generated, is increased to provide adequate illumination within the oven cavity.